Method of suppressing water and gas coning in oil wells



March 12, 1957 c. s. MATTHEWS ETAL 2,784,787

METHOD OF SUPPRESSING WATER AND GAS CONING IN OIL WELLS Filed Aug. 11,1953 3 Sheets-Sheet 1 THEE STRATA FIGL'Z.

March 12, 1957 c. s. MATTHEWS ETAL 2,784,787

METHOD OF SUPPRESSING WATER AND GAS comma IN OIL WELLS Filed Aug. 11,1953 3 Sheets-Sheet 2 l6 SEALJNG MxramAL.

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METHOD OF SUPPRESSING WATER AND GAS CONING IN OIL WELLS Filed Aug. 11,1955 5 Sheets-Sheet 5 On.. oz OTHER FLUID SEALJNE; MATERIAL.

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METHOD OF SUPPRESSING WATER AND GAS I CONING IN OIL WELLS Charles S.Matthews and James W. Killian, Houston,

Tex., assignors to Shell Development Company, Emeryville, Calif., acorporation of Delaware Application August 11, 1953, Serial No. 373,640

7 Claims. (Cl. 166-21) This invention relates to the treatment of oilWells, and

pertains more particularly to improved methods of treating formations ofwells producing both oil and water, whereby a watenbearing portion orzone of the formation may be sealed or isolated from the oil-bearingportion or through various stages until finally the well may beproducing large quantities of liquid of which but a small First, some ofthe waterfrom the lower zone may finger up into the oil-producing zonebefore entering the borehole; then, as the flooding advances, the

Water rises higher and higher in the oil-producing sand adjacent to theborehole and reduces more and more the flow area by which the oil mayenter the well borehole. This process may continue tosuch an extent thatthe production from thewell is largely water even though a significantquantity of oil may remain in the formation. Production ofthis oil maynot be economically feasible at the very reduced oil rate caused by thewater influx into the .well bore.

Thismigration of water from a lower portion or zone of theformationintothe producing section of the formation adjacent the wellborehole is known as coning of water. The formation of such a coneincreases the flow area for the water at the expense of the how area forthe oil thelrate at which thistakes placedepending largely upon .thecharacterof the formation, the character of the fluids therein and therate of production. This may result in the almost complete saturationwith water of the sands adjacent the :well, most of the oil gainingaccess-to the well as globules that have to pass through the water. Whenthis condition is attained, methods generally used in the petroleumindustry for attempting to cope with the influx of Water have met withlittle degree of success.

Several methods of suppressing water coning in wells producing both oiland water have been suggested. For

example, the most obvious method consisted of depositing cement in thewell borehole adjacent the water-producing formation up to the interfacebetween the water-producing and oil-producing zones. This remedy provedineffective as the water from the lower zone continued to intrude intothe oil-bearing zone adjacent the borehole. In another attempt toprevent water coning, a packer was set in the borehole at the interfacebetween the oil-bearing zone and the adjacent water bearing zone, and asealing material was forced down a tubing and through the packer intothe space below which was adjacent the water-producing zone. Pressurewas then applied to the column of plastic sealing material toforce theimpervious material into the water-bearing zone to seal it offeffectively. While the 2,784,787 Patented Mar. 12, 1957 2 imperviousmaterial expanded radially from the borehole into the formation to sealoff the water-bearing zone, some of the material was also forced bothradially and upwardly into the oil producing zone thereby diminishingthe effective production area of the well.

Other workers in the field have suggested introducing into the wellborehole and positioning therein adjacent to the oil-producing zoneeither a stagnant fluid or a gel-like mass which would prevent thematerial used to seal the water zone from contaminating the oilproducing formation. The use of a stagnant liquid in such a manner,however, did not prevent the intrusion of a mass of sealing materialfrom the water-producing zone into the oil-producing zone. Further, ithas been suggested to crack the producing formations at the interface ofthe oil-bearing zone and water-bearing zone and to inject into thecracked formation a thin layer of cement or other impervious materialextending radially from the borehole. The difiiculty with this method isthat it is usually not possible to crack the formation in the desireddirection for any appreciable distance.

It is therefore a primary object of this invention to provide a methodfor suppressing water coning into well boreholes.

A further object of this invention is to provide a method forsuppressing water coning into well boreholes having both oil andwater-producing zones without contaminating the oil-producing formation.

Another object of this invention is to provide a method for suppressingwater coning in a well borehole having both oil and water-producingzones without appreciably reducing theeifective producing area of theoil-producing formation. i

It is also a further object of this invention to provide a method forsuppressing water coning into a well borehole having both oil andwater-producing zones by sealing or isolating the water-producing zonefrom the oil-producing zone at apoint adjacent the borehole.

Another objectof this invention is to provide a method for suppressing-water coning in a well borehole having both ,water and oil-producingzones by effectively sealing off the water-producing zone of the wellwhile preventing the sealing material from entering the oil-producingzone.

Still another object of this invention is to provide a method forreducing the water/ oil production ratio in a well havinglboth oil andwater-producing formations.

Anotherobject of this-invention is to provide a method for reducing gasconing.

.A further object of this invention is to provide a method for reducingthe gas-oil production ratio in wells witha gas cap.

. These and other objects of this invention will be understood from thefollowing description taken with reference to the attached drawing,wherein:

Figure 1 is a vertical section through a. well borehole diagrammaticallyillustrating the formation of a water cone around an oil well.

Figure 2 is avertical section through a well borehole diagrammaticallyshowing equipment whereby a sealing material is being injected into thewater zone of the well borehole, with a portion of the plugging materialballooning upwardly intothe oil zone.

Figure 3 is a vertical section through a well borehole diagrammaticallyillustrating the injection. of a plugging material into thewater-producing zone while injecting a non-plugging fluid or materialinto the oil-producing zone.

Figures .4 and 5 are vertical sections through a well boreholediagrammatically illustrating two different methods for injecting a diskof plastic or other sealing material radially into thelformation atapoint substantially at the interface of the oil and water-bearingformations.

Referring to Figure 1 of the drawing, a well borehole 11 is shown whichhas been drilled through various strata including a formation orformations having an oil-producing zone 12 and a Water-producing zone 13which underlies the oil zone. The well casing 14 is shown as positionedin the borehole 11, being sealed therein by cement 15. Depending withinthe well casing 14 is the lower end of a production tubing 16.

The actual contact or transition zone represented by line 17 whichseparates the oil-bearing formation 12 from the water-bearing formation13 varies in degree of abruptness but is usually characterized by lowwater saturation in the lower part of zone 12 and in the upper part ofzone 13 with progressive increase in water saturation with depth belowthe oil-water contact zone along the line 17.

Area 18 is a diagrammatical representation of what is commonlydesignated as a Water cone around the well borehole 11 in theoil-bearing formation producing both oil and water. Within such area 18,the natural oilwater saturations have been greatly modified by waterencroachment and the formation thus represented has become morepermeable to water than to oil. Water from the water-bearing zone 13 hasmoved upwardly into the oil-bearing formation 12 adjacent the wellborehole 11, thus reducing the depth of the oil sands at the wall of theborehole 11 from its original depth A to its present depth B. Continuedenlargement of the water cone 18 by further upward migration of theWater into the oil bearing zone 12 would ultimately cause the oil sands12 adjacent the borehole to become flooded with water thus efiectivelyshutting off the entrance of oil from zone 12 into the borehole 11.

In an attempt to prevent water coning, the lower waterbearin g formation13 is often sealed off by depositing a volume of plastic at the bottomof the borehole and injecting it into the adjacent water-bearing zone13. As shown in Figure 2 of the drawing, a well packer 21 may be mountedon the lower end of a pipe string 16 and lowered into the well to thelevel of the interface between the oil and water-bearing zones where itis sealed against the walls of the well casing or borehole. A sealingmaterial in then pumped down the pipe string 16 and forced underpressure into the Water-bearing formation 13. A sealing plug 22 isformed around the borehole by the sealing material which is forced intothe formation. It is to be noted that the sealing material besidesexpanding radially into the formation is also forced upwardly into theoil-bearing formation 12 around the packer 21.

This movement of sealing material upwardly into the oil zone 12 aroundthe packer 21 is known as ballooning.

The present invention may be practiced to suppress water coning in awell producing both oil and water and to prevent the ballooning of asealing material injected into'the well to seal off the water-bearingzones. In accordance with the present invention a pipe string 16, havinga packer 21 attached to the lower end thereof, is lowered into a wellborehole 11 as shown in Figure 3 and the packer 21 is set against thewalls of the borehole at above or below the interface of the oil andwater-bearing zones 12 and 13, respectively. A fluid plastic or otherimpervious material is pumped down the pipe string 16 into the bottom ofthe borehole 11 where it is forced radially into the adjacentwater-bearing formation under pressure to effectively seal thewater-bearing formation adjacent the borehole by forming a sealing plug22.

Simultaneously, a second fluid, which is non-sealing in character, isforced down the annulus 23 between the Well casing 14 and the pipestring 16. The non-sealing liquid is forced radially into theoil-producing zone 12. Any suitable non-sealing material which will notcontaminate or block the oil sands 12 may be used to prevent theballooning of the sealing material. The most common non-sealing fluidwhich could be used would, of course, be some of the oil which hadalready been produced by that well.

Chemicals or other materials which control the viscosity of the oil maybe added to the oil to alter its viscosity. Radial velocities of thenon-sealing oil into the oil zone and of the plastic sealing fluid intothe water zone can be maintained equal and parallel to the interface 17provided that a proper relationship is maintained between thepermeabilities of the two zones 12 and 13 and the viscosities andinjection pressures of both fluids. The permeability of the oil sand 12to the non-sealing fluid and of the water sand 13 to the sealing fluidcan be readily determined in a manner well known to the art after coresfrom each zone have been obtained as by a sidewall coring operation.After determining the permeabilities of the sands of the two zones, theviscosities of the sealing fluid and/ or of the non-sealing fluid may beadjusted, as by the addition of chemicals, other oils, or othermaterials, so that the two fluids pass through the respective formationsat equal radial velocities when they are injected into the well underpressure greater than formation pressure and so adjusted that thepressure in the non-sealing fluid just above the packer is equal to thepressure in the sealing fluid just below the packer. If the formationcontaining the oil and/ or water-producing zone is not homogeneouslypermeable, the adjustment should be made to maintain equal radialvelocity at the sealing/non-sealing fluid interface.

Alteration of the viscosity of the non-sealing fluid is not essential ifsome contamination of the oil zone is allowable. The basic steps in thepresent invention comprise the simultaneous injection of the two fluids,although alteration of non-sealing fluid viscosity may be desirable inmany cases. When the well is put on production, the oil in the oil sand12 forces the non-sealing liquid out of the sand and into the boreholewhere it is raised ahead of the normal well fluid.

The suppression of water coning may also be readily accomplished bycarrying out the present method as diagrammatically illustrated inFigure 4 of the drawing. In this modification, the coning of water froma lower waterproducing zone 13 to the upper oil-producing zone 12 may besuppressed by forming either in the oil zone 12 or between the two zones12 and 13 at a point adjacent the borehole 11, a disk 24 of plastic orother impervious material, which will solidify after being forced intoplace. To form the disk 24 a pipe string 16 is lowered into the wellborehole 11, there being carried on the lower end of said pipe string 16is spaced relationship a pair of packers 25 and 26. The packers 25 and26 are adapted to be sealed against thewall of a borehole, while thespace above the packers is in communication with the space therebelowthrough a suitable conduit means such as a short pipe 27 extendingthrough both packers 25 and 26. The space 28 between packers 25 and 26is in communication with the bore of the pipe string 16 through one ormore suitable ports 29 in the lower end of the pipe string. The bottomof the pipe string is closed in any suitable manner as by a cap or plug30.

The disk 24 shown in Figure 4 may be formed by placing the doublepackers 25 and 26 in the borehole 11 so as to straddle the desired levelat which the plastic is to be placed. While the plastic disk 24 ispreferably injected and formed at the interface between the oil andwaterbearing zones, the plastic may, however, be injected above or belowthe interface. Thus, it may be desirable in many cases to inject theplastic entirely in the oil-bearing zone. This should postpone coningeven longer than injection at the interface. As the water level risesand passes over this first plastic disk, coning may begin anew. If asufficient thickness of oil-bearing formation is left it may then befeasible to set a second plastic disk above the water layer. Possibly amulti-disk device could be used to inject several disks at one time,then as water encroached, a borehole packer or plug could be used toseal each disk at the well bore. The plastic could be injected at thetime the well was completed if thought desirable. Prior to the placementof these packers 25 and 26, the formations at this level may befractured as by shooting with explosives, or may be cut as by reaming,undercutting, or in any other manner well known to the art. Afterplacement of the packers in position, a sealing material is forced downpipe string 16 out ports 29 into the space 28 between the packers 25 and26 and thence into the formation between the oil zone 12 and the waterzone 13 to form a diskshaped deposit of material 24 which readilyhardens or solidifies to become impervious to water. Simultaneously, oilor any other non sealing material is forced down the annulus 23, aportion of the non-sealing material being forced into the oil-producingzone 12, while the other portion of the non-sealing material is forcedthrough conduit 27 by-passing the packers and thence into thewaterproducing formation 13. By maintaining a flow of nonsealing fluidinto the formation in a direction essentially parallel to the interfaceand at a radial velocity equal to that at which the sealing materialflows into the formation, a disk 24 of suitable lenticular shape may beformed without any of the material ballooning upwardly into the oilformation or downwardly into the water formation. Such a flow may bemaintained by suitable adjustment of fluid viscosity as discussed aboveand by maintaining pressures above and below the packers nearly equal.The thickness of the disk 24 may vary from several inches to severalfeet, depending on the character of the formations and the pressures andviscosities used.

As a substitute for the oil or other non-sealing fluid to be used in theregion below the plastic disk 24, i. e., adjacent the water-bearingformation 13, water treated with viscosity-increasing chemicals, such asglycerol or sugar may be used. The apparatus needed to inject threedifferent fluids into a well borehole would be modified slightly asshown in Figure of the drawing to include a small diameter pipe string32 positioned within the pipe string 16 and extending through the plug30 closing the lower end of said pipe string.

Thus, by using the equipment shown in Figure 5 of the drawing, oil orany other non-sealing fluid is pumped down the annulus 23 between thewell casing 14 and the pipe string 16 to be injected into theoil-producing formation 12 while at the same time the sealing materialis pumped down the pipe string 16 and forced into the formation to forma disk 24 and a third fluid, preferably an inexpensive fluid, is forceddown the inner pipe string 32 and into the water-producing formation 13.The pump pressures and the viscosities of the fluids may be adjusted(dependent upon the permeabilities of the formation(s) to the injectedfluids) so that the radial velocity of all three fluids into theformations is substantially equal and in a direction parallel to theinterface 17.

While best results are obtained when the velocities of all the fluidsbeing injected are equal it is not essential to the prevention of coningthat the radial velocities of all three fluids be equal. A curved orotherwise distorted disk will also suppress coning though, possibly, atsome sacrifice in efficiency.

Any suitable sealing material may be employed according to the presentinvention which may be injected into a formation and form therein awater-impermeable mass. Among the various materials which may be usedare many resins, synthetic resins, plastics, synthetic plastics, such asphenol formaldehyde and urea formaldehyde resins, various gels such assilica gel, various gums such as Yacca gum, mixtures of asphalt andpyridine, and the like. The materials used should be both water and oilinsoluble.

After a sealing material has been forced into the formation, theremainder of the sealing material and/or nonsealing material may beremoved from the casing 14 or the pipe strings 16 and 32 in any mannerwell known to the art, as by circulation. if the packers 21, 25, and 26are removed from the borehole together with the pipe strings, they arepreferably replaced by other packers in a manner well known to the artto prevent water from a water-bearing formation frommixing with oil inthe well borehole.

We claim as our invention:

1. In a well borehole traversing an oil-bearing formation and otherformations adjacent thereto containing undesirable fluids, the method ofsuppressing the migration of a fluid from said other formations into theoil bearing formation adjacent the borehole, said method comprisingpacking off-the section of borehole adjacent the formation to be sealed,injecting a fluid. water and oil insoluble sealing material underpressure radially into the formation adjacent the packed'off section ofborehole, simultaneously injecting a non-sealing liquid under pressureradially into at least said oil-bearing formation traversed by saidborehole, both of said injections being carried out at pressuressufficient to maintain the radial flows of the fluid sealing materialand non-sealing fluid into the forma tions at substantially equalvelocities, and subsequently reopening the oil-bearing formation toproduction.

2. In a well borehole traversing an oil-bearing formation and awater-bearing formation, the method of preventing the migration of waterfrom the water-bearing formation into the oil-bearing formation adjacentthe borehole, said method comprising packing oil a portion of theborehole at a level between the two formations, injecting a water andoil insoluble sealing fluid into said packed-off portion of saidborehole and radially into the water-bearing formation, simultaneouslyinjecting, radially into said oil-bearing formation a nonasealingliquid, both of said injections being carried out at pressuressuflicient to maintain the radial flows of the sealing fluid andnon-sealing liquids into the formations at substantially equalvelocities, and subsequently reopening the oil-bearing formation toproduction.

3. In a well borehole traversing an oil-bearing formation and awater-bearing formation, the method of preventing the migration of waterfrom the Water-bearing formation into the oil-bearing formation adjacentthe borehole, said method comprising packing off a portion of theborehole between two levels vertically spaced from each other substantially at the interface between the two formations, injecting to aradial depth equal to at least the diameter of the borehole a water andoil insoluble sealing liquid into said packed-off portion of saidborehole and into the formation substantially at the interface of saidoil-bearing and water-bearing formations, simultaneously injecting anon-sealing liquid into said oil-bearing formation and through saidpacked-off portion of said borehole into said Water-bearing formation,both of said injections being carried out at pressures sufliicient tomaintain the radial flows of the sealing and non-sealing liquids intothe formations at substantially equal velocities, and subsequentlyreopening the oil-bearing formation to production.

4. In a well borehole traversing an oil-bearing formation and awater-bearing formation, the method of preventing the migration of waterfrom the water-bearing formation into the oil-bearing formation adjacentthe borehole, said method comprising fracturing the borehole wall atsubstantially the interface of said oil-bearing and water-bearingformations, packing off the fractured portion of the borehole, injectingunder high pressure a water and oil insoluble sealing liquid into saidpacked-off portion of said borehole and into the formation fracture,simultaneously injecting into said oil-bearing formation a nonsealingliquid, both of said injections being carried out at pressuressufiicient to maintain the radial flows of the sealing and non-sealingliquids into the formations at substantially equal velocities, andsubsequently reopening the oil-bearing formation to production.

5. In a well borehole traversing an oil-bearing formation and awater-bearing formation, the method of preventing the migration of waterfrom the water-bearing formation into the oil-bearing formation adjacentthe borehole, said method comprising packing ed a portion of theborehole between two levels vertically spaced from each othersubstantially at the interface between the two formations, injecting awater and oil insoluble sealing liquid into said packed-off portion ofsaid borehole and into the formation substantially at the interface ofsaid oil-bearing and water-bearing formations, simultaneously injectinga first non-sealing liquid into said oil-bearing formation,simultaneously injecting a second non-sealing liquid through saidpacked-off portion of said borehole into said water-bearing formation,said injections being carried out at pressures sufiicient to maintainthe radial flows of the sealing and non-sealing liquids into theformations at substantially equal velocities, and subsequently reopeningthe oil-bearing formation to production.

'6. In a well borehole traversing an oil-bearing formation and awater-bearing formation, the method of preventing the migration of waterfrom the water-bearing formation into the oil-bearing formation adjacentthe borehole, said method comprising packing of). a portion of theborehole between two levels vertically spaced from each othersubstantially at the interface between the two formations, injecting awater and oil insoluble sealing liquid into said packed-01f portion ofsaid borehole and into the formation substantially at the interface ofsaid oil-bearing and water-bearing formations, simultaneously injectinga non-sealing hydrocarbon base liquid into said oil-bearing formation,simultaneously injecting a non-sealing waterbase liquid through saidpacked-01f portion of said borehole into said water-bearing formation,said injections be- Q p U V ingcarried out at pressures sufiicient tomaintain the radial flows of the sealing and non-sealing liquids intothe formations at substantially equal velocities, and subsequentlyreopening the oil-bearing formation to production.

7. In a well borehole traversing an oil-bearing formation and awater-bearing formation, the method of preventing the migration of Waterfrom the water-bearing formation into the oil-bearing formation adjacentthe borehole, said method comprising fracturing the borehole wallsubstantially at the interface'of said oil-bearing and Waterbearingformations, packing 01f above and below the fractured portion of theborehole, injecting under high pressure a water and oil insolublesealing liquid into said packedoff portion of said borehole and into theformation fracture, simultaneously injecting a non-sealing liquid intosaid oil-bearing formation and through said packed-off portion of saidborehole into said Water-bearing formation, both of said injectionsbeing carried out at pressures sufiicient to maintain the radial flowsof the sealing and non-sealing liquids into the formations atsubstantially equal velocities, and subsequently reopening theoil-bearing formation to production.

References Cited in the file of this patent UNITED STATES PATENTS2,258,616 Kendrick Oct. 14, 1941 2,368,424 Reistle Jan. 30, 1945

1. IN A WELL BOREHOLE TRAVERSING AN OIL-BEARING FORMATION AND OTHERFORMATIONS ADJACENT THERETO CONTAINING UNDESIRABLE FLUIDS, THE METHOD OFSUPPRESSING THE MIGRATION OF A FLUID FROM SAID OTHER FORMATIONS INTO THEOILBEARING FORMATION ADJACENT THE BOREHOLD, SAID METHOD COMPRISINGPACKING OFF THE SECTION OF BOREHOLE ADJACENT THE FORMATION TO BE SEALED,INJECTING A FLUID WATER AND OIL SOLUBLE SEALING MATERIAL UNDER PRESSURERADIALLY INTO THE